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Re: 11th specimen of Archaeopteryx



Scott Hartman wrote:

>In the absence of any other supporting data it's just special
> pleading to keep trying to explain away the foot anatomy as somehow
> "not preventing" an arboreal lifestyle.

Wouldn't it be more accurate to say that studies on the toes of
Archaeopteryx and Microraptor have mixed results?

Also, please note, I'm not advocating an arboreal lifestyle. I've only
looked to roosting, like we see today in many ground - based birds, as one
hypothetical model for the origins of arboreality in paravians.

Forgive me if you have already refuted these sources, and I know that one
recent paper did contradict them, but allow me to mention two examples
from the literature:

 Hopson (2001) found that Archaeopteryx had toe proportions that fell in
the overlap between terrestrial and arboreal birds, with those which
forage on the ground.

Glen and Bennet (2007) studied toe claw curvature and found that the
values for some specimens of both Microraptor and Archaeopteryx fell in
the ground foraging (exemplified by pigeons and doves) range while others
were in the ground - based range.



>> Not to pounce on this one sentence, but I simply don't agree that this
>> is> how evolution works. There are myriad cases where we might expect
>> an> anatomical adaptation, where one would make sense, but we do not get
>> one.> It is not true that there must be an "excuse".
>
> Sure, but we also have to let the evidence drive our inferences, not
> the other way around.  Not only is the hallux of Archaeopteryx too
> high and not reversed, but none of the toe claws have the tubercle
> morphology seen in perching birds, the toe proportion do not match
> perching birds, and there is no ventral curvature in the pedal
> phalanges as seen in perching birds.
>

>
> -Scott
> On Tue, Nov 1, 2011 at 11:35 PM, Jason Brougham <jaseb@amnh.org> wrote:
>> Tim Williams wrote:
>>>
>>> If _Archaeopteryx_, microraptorines etc were roosting in trees,
>>> there's simply no excuse for *not* having a hallux that was low enough
>>> and large enough to grip branches - ideally combined with at least
>>> some reversal of the hallux, for the pes to be capable of some kind of
>>> opposable grip.
>>
>> Not to pounce on this one sentence, but I simply don't agree that this
>> is
>> how evolution works. There are myriad cases where we might expect an
>> anatomical adaptation, where one would make sense, but we do not get
>> one.
>> It is not true that there must be an "excuse".
>>
>> just as one quick and pedestrian example, there is no "excuse" for
>> mammals
>> to have external testis which descend into a scrotum seeking the lower
>> temperatures that provide more efficient spermatogenesis. Birds adapted
>> to
>> endothermy and were able to keep their testis inside the abdomen, where
>> they are far less prone to injury.
>>
>>
>>
>>
>>
>
>
>
> --
> Scott Hartman
> Scientific Advisor/Technical Illustrator
> (307) 921-9750
> website: www.skeletaldrawing.com
> blog: http://skeletaldrawing.blogspot.com/
>


Jason Brougham
Senior Principal Preparator
Department of Exhibition
American Museum of Natural History
81st Street at Central Park West
212 496 3544
jaseb@amnh.org